This invention relates to structural members.
In a previously filed application, an invention was disclosed relating to rods and shafts which are suitable for use in the construction of tapered and parallel edged fishing rods, golf shafts, yacht masts, sailboard masts and the like.
Fishing rods, golf shafts, yacht masts, sailboard masts, and the like are generally constructed of fibre-resin composites or metal in the form of solid rods or tubes. Hollow composite rods are accepted as being superior in performance to solid composite rods in light weight uses but they are delicate and easily damaged. Solid metal rods and metal tubes are generally inferior in flexural characteristics to the composite rods. It will be apparent to the skilled person that the teaching of rod or shaft construction in the above arts may be effectively applied to other heavier, industrial or civil engineering uses as well.
Tapered, tubular composite rods require expensive, accurately ground metal mandrels to produce the taper necessary for the desired performance and there are considerable difficulties in manufacturing with uniform wall thickness. An attempt to overcome to some extent the problems associated with tubular rod manufacture from composite materials is the subject of U.S. Pat. Nos. 4,582,758 and 5,229,187 (referred to herein respectively as Bruce & Walker and McGinn), the enabling teaching of which are incorporated herein.
Both patents relate to the provision of rods of polygonal cross-section formed by a plurality of elements of certain geometrical cross-section. Bruce & Walker describes that each of the elements has a base part of a fibre reinforced plastic material and an apex of part of a rigid plastic material foam.
McGinn, on the other hand, adopted a method of using T-sections made from fibre reinforced plastic material. The method by which the joints of the top ends of T-sections in McGinn are joined is shown in FIG. 5 of that patent. It is seen that the top ends of the T-sections must be molded or machined to a relatively small tolerance to accommodate matching of the several faces of the T-sections to each other. Both these rods, while they solve wall thickness variation problems and obviate the need for expensive mandrels for forming are difficult to make in the required thickness.
Bruce & Walker experience difficulties in the required stiffness for heavy load application such as are encountered in deep sea fishing and similar application without resorting to excessive composite wall thickness. The technology applied by McGinn addresses the stiffness required in heavy load application, but the mere nature of this technology reduces the ability to make the rods flexible for fly rod application in the various line weights required. Neither invention has adequately addressed the problem of torque encountered in small structures such as golf shafts.
The problem is severe in the case of Bruce & Walker. The McGinn technology has gone some way to addressing this problem with sufficient torque being removed from fishing rods to make them user acceptable. However, the problem of torque is highlighted when both products are used as golf shafts. Any torque in the shafts alters the angle of the golf club head when it comes in contact with the ball, which is unacceptable to the playing golfing public.
It is therefore one object of the present invention to provide a rod, shaft, etc., which obviates or at least minimizes the aforementioned disadvantages of conventional rods and those of Bruce & Walker and McGinn.